The mechanism of acuity reduction and the site of involvement in amblyopia are not well understood. Behavioral and electrophysiological data obtained from cats and monkeys deprived of normal visual experience due to lid suture or strabismus during the critical period suggest that there is a severed disruption of visual function and that physiological and morphological changes occur. The proposed research is an application of psychophysical technique to the better understanding of amblyopia through the characterization of the vision of specially reared rhesus monkeys and of naturally occurring human amblyopes. Contrast sensitivity functions will be behaviorally determined in control monkeys and monkeys reared with monocular lid suture or strabismus through the critical period. The effect of stimulus duration, frequency and luminance levels will be investigated. Similar experiments will be conducted on human amblyopes to determine the adequacy of the monkey as an animal model of naturally occurring amblyopia in humans.